1. Technical Field
The present invention relates to image analysis, and more particularly to a system and method for volume sampling.
2. Discussion of Related Art
Processing of data to determine a feature value or to generate new data is typically done on a sub-volume rather than the entire volume of data, e.g., a 3-dimensional computed tomography (CT) scan. Typically the sub-volumes are extracted from the original volume in such a way that the sampling frequency of the sub-volumes does not match that of the original volume. For example, some algorithms might require the sub-volumes to be isotropic whereas the original volume might not be isotropic or be isotropic at a different resolution. In such cases, the sub-volume is extracted from the original volume by sampling the original volume at a given sampling frequency. Due to this sampling the voxels in the original volume do not have a one-to-one correspondence to the voxels in the sub-volume.
When multiple sub-volumes are extracted from an original volume, the sub-volumes typically overlap. FIG. 1 shows an example of overlap. The original volume is shown as a border 101. Two sub-volumes 102 and 103 are extracted from this volume. Assume that the algorithm processing the sub-volumes is extracting a feature on a region-of-interest (ROI) 104. This region of interest 104 can be common to the two overlapping sub-volumes 102 and 103 as shown in FIG. 1. Ideally, a determined feature value for two or more sub-volumes should be identical if they include identical portions of a ROI inside them. Similarly, when the identical portions of the ROI inside the sub-volumes are visualized, they should look identical.
In practice the feature value computed on the two sub-volumes may differ and the visualization of the two sub-volumes may look different. The reason for the difference is as follows. When a first sub-volume is extracted, the original volume is sampled to get a desired sampling frequency of the sub-volume. When a second sub-volume is extracted, the sampling process is repeated. By observing the sample locations of the two sub-volumes inside the original volume, it can be determined that the sample locations for both of the sub-volumes do not match in the area where they overlap. For example, see FIG. 2 in which sample locations for the first and second sub-volumes 202 and 203, respectively, are equidistant, but do not match. As a result, the voxel values in the common region of the two sub-volumes differ. This difference in voxel values results in difference in the determined feature value.
FIG. 2 shows sampling locations of two overlapping sub-volumes. The lines 201 represent locations of the original samples, the lines 202 represent the sample locations of the first sub-volume and the lines 203 represent the sample locations for the second sub-volume. It can be observed that the sample locations of the two sub-volumes 202 and 203 do not match. This leads to feature values that are not identical for the two sub-volumes.
Therefore, a need exists for a system and method for synchronized sampling of multiple sub-volumes wherein the sampling locations are identical in the area where the sub-volumes are overlapping.